DatapointLabs Technical Center for Materials has a mission to strengthen the materials core of manufacturing enterprises by facilitating the use of new materials, novel manufacturing processes, and simulation-based product development. A whole-process approach is needed to address the role of materials in this context.

Physically accurate simulation is a requirement for initiatives such as late-stage prototyping, additive manufacturing and digital twinning. The use of mid-stage validation has been shown to be a valuable tool to measure solver accuracy prior to use in simulation. Factors such as simulation settings, element type, mesh size, choice of material model, the material model parameter conversion process, quality and suitability of material property data used can all be evaluated. These validations do not use real-life parts, but instead use carefully designed standardized geometries in a controlled physical test that probes the accuracy of the simulation. With this a priori knowledge, it is possible to make meaningful design decisions. Confidence is gained that the simulation replicates real-life physical behavior. We present three case studies using different solvers and materials, which illustrate the broad applicability of this technique.

With the advent of 3D printing and additive manufacturing, manufacturing designs previously thought difficult to produce can now be generated quickly and efficiently and without tooling. In the aerospace industry, weight is often tied directly to cost and is thus of great importance to any engineering design. Traditionally, the design process often involves much iteration between the designer and the analyst, where the designer submits a design to the analyst, and then the analyst completes his or her analysis and sends recommendations back to the designer. The process is repeated until a valid design meets the analysis criteria. The design is then handed to the manufacturing team which then may have additional constraints or concerns and iterations can continue. Additive manufacturing coupled with topology optimization allows the design and analysis loops and manufacturing iterations to be reduced significantly or even eliminated. The critical step is to ensure that the part will perform as simulated.

This book is intended to be a companion to the NAFEMS book, "An Introduction to the Use of Material Models in FE". It informs Finite Element Analysis users of the manner and methodologies by which materials are tested in order to calibrate material models currently implemented in various FEA programs. While the authors seek first to satisfy the basic material models outlined in the companion book, they make important extensions to FEA used in currently active areas including explicit simulation.

"In sheet-metal-forming the forming limit curve (FLC) is used for ductile sheets to predict fracture in deep drawing.
However the use of the FLC is limited to linear strain paths. The initial FLC cannot be used in a complex nonlinear
strain history of a deep drawing process or a successive stamp and crash process including a significant change in
strain rate. The CRACH software has been developed to predict the forming limit of sheets for nonlinear strain paths
[1]. It has been validated to predict instability for bilinear strain paths with static loading in the first path and
dynamic loading in the second path for mild steels [2].
As the postprocessing of strain paths from single finite elements in CRACH is not economic for industrial
applications MATFEM initiated a project to couple CRACH directly with FEM-Code LS-DYNA using a userdefined
material model. This allows a prediction of possible failure during the simulation for all elements with
respect to their complete strain history. A special strategy has been developed to include CRACH without extensive
increase in total CPU time. The developed interface to LS-DYNA allows also the implementation of other failure
criteria demanding the history of deformation like for example a tensorial fracture criterion.
In order to test the reliability of the calculated safety factor experimental tests for bilinear strain paths have been
simulated [2]. In this case the experimental and numerical investigations have been made on two-stage forming
processes (static in the 1st stage and both static/dynamic in the 2nd stage) . The static-static case should simulate a
stamping process with bilinear strain path. The static-dynamic case should simulate a successive stamp and crash
process.
The simulation of a complex deep drawing problem including areas with significantly nonlinear strain paths has
been simulated with LS-DYNA/CRACH-coupling. It can be shown that the prediction of CRACH can differ
significantely from a “standard” prediction based on the initial FLC.
The coupling of LS-DYNA and CRACH showed the potential to predict possible fracture in deep drawing and crash
loading at an early design stage and allowed to optimise geometry and material quality to significantly reduce later
problems in real components."

"Today the automotive industry is faced with the demand to build light fuel-efficient vehicles while
optimizing its crashworthiness and stiffness. A wide variety of new metallic and polymeric materials
have been introduced to account for these increased requirements. Numerical analysis can
significantly support this process if the analysis is really predictive. Within the numerical model a
correct characterization of the material behaviour – including elasto-viscoplastic behaviour and failure
- is substantial. The particular behaviour of each material group must be covered by the material
model.
The user material model MF GenYld+CrachFEM allows for a modular combination of
phenomenological models (yield locus, strain hardening, damage evolution, criteria for fracture
initiation) to give an adequate representation of technical materials. This material model can be linked
to LS-DYNA when using the explicit-dynamic time integration scheme.
This paper gives an overview on the material characterization of ultra high strength steels (with focus
on failure prediction), non-reinforced polymers (with focus on anisotropic hardening of polymers), and
structural foams (with focus on compressibility and stress dependent damage evolution) with respect
to crash simulation. It will be shown that a comprehensive material model - including damage and
failure behaviour - enables a predictive simulation without iterative calibration of material parameters.
A testing programme has been done for each material group in order to allow a fitting of the
parameters of the material model first. In a second step different component tests have been carried
out, which were part of a systematic procedure to validate the appropriate predictions of the crash
behaviour with LS-Dyna and user material MF_GenYld+CrachFEM for each material group."

"The Crash Simulation of Magnesium Structures with Finite Element Methods demands
the use of suitable material and failure models. An associated plasticity model
describing the complex asymmetric yield behaviour in tension and compression of
Mg extrusions has been developed during the InMaK-project (Innovative Magnesium
Compound Structures for Automobile Frames) supported by the German Federal
Ministry for Education and Research (BMBF). Differences to the material model 124
in LS-DYNA are exposed. In order to describe the failure behaviour of Mg extrusions
under multiaxial loading in FEM crash simulation this constitutive model has been
combined with a fracture model for ductile and shear fracture. The fracture model
has been added to the user defined constitutive magnesium model in LS-DYNA. The
experimental investigations carried out on model components are compared with
numerical derived results. Experimental methods for fracture parameter evaluation
are shown and general aspects of metal failure due to fracture as well as different
modelling techniques are discussed."

FAA William J Huges Technical Center (NJ) conducts a research project to simulate failure in aeroengines and fuselages, main purpose is blade-out containment studies. This involved the implementation in LS-DYNA of a tabulated generalisation of the Johnson-Cook material law with regularisation to accommodate simulation of ductile materials.

"Heavy trucks have large masses and only small deformation zones. Because of this, they are loaded
relatively severe in case of a crash. Under those conditions structural response is characterised not
only by plastic deformation but also by failure in terms of cracks or fracture. Hence, failure prediction is
essential for designing such parts.
The following article describes the procedure of generating material models for failure prognosis of
solid parts in the Commercial Vehicles Division at Daimler.
Sheet metal parts are mostly discretised by shell elements. In this case the state of stress is
characterized by hydrostatic pressure over von-Mises effective stress, the so-called triaxiality. For
many real-life load cases which can be modeled by thin shells this ratio is between –2/3 and –2/3.
Within this range the Gurson material model with the Tvergaard Needlemann addition leads to
sufficiently accurate results. Furthermore, the Gurson material model allows considering the effect of
element size, which amongst others is important for ductile materials.
Most often however, in the case of solid parts the state of stress is more complex, which results in a
triaxiality smaller than –1 or larger than 2/3. Gurson material models are usually validated based on
shell meshes and tensile tests with flat bar specimen. If applied to solid parts, these models tend to
underpredict failure . Thus, for solid parts the GURSON_JC material model is used.
The Johnson Cook parameters are derived from an existing Gurson material model. Afterwards the
material model is adapted to test results by modifying the load curve giving failure strain against
triaxiality. This requires tensile tests"

"To assess the problem of containment after a blade-off accident in an aero-engine by numerical
simulation the FAA has instigated a research effort concerning failure prediction in a number of
relevant materials. Aluminium kicked off the program which involved an intensive testing program
providing failure data under different states of stress, different strain rates and different temperatures.
In particular split Hopkinson bars were used to perform dynamic punch tests on plates of different
thicknesses allowing to investigate the transition between different failure modes such as petaling and
plugging. Ballistic impact tests were performed at NASA GRC for the purpose of validation.
This paper focuses on the numerical simulation effort and a comparison with experimental data is
done. The simulations were performed with LS-DYNA and a tabulated version of the Johnson-Cook
material law was developed in order to increase the generality, flexibility and user-friendliness of the
material model."

Generating a LS-DYNA material model from cupon-level quasi-static experimental data, developing appropriate failure characteristics, and scaling these characteristics to mesh sizes appropriate for a variety of simulation models requires a regularization procedure. During an Investigation of an anisotropic material model for extruded aluminum, numerical accuracy issues led to unrealistic mesh regularization curves and non-physical simulation behavior. Sensitivity problems due to constitutive material behavior, small mesh sizes, single precision simulations, and simulated test velocity all contributed to these accuracy issues. Detailed analysis into the sources of innaccuracy led to the conclusion that in certain cases, double precision simulations are necesscary for accurate material characterization and mesh regularization.

LS-DYNA software contains a wealth of material models that allow for the simulation of transient phenomena. The Matereality® CAE Modeler is a generalized pre-processor software used to convert material property data into material parameters for different material models used in CAE. In a continuation of previously presented work, we discuss the extension of the CAE Modeler software to commonly used material models beyond MAT_024. Software enhancements include advanced point picking to perform extrapolations beyond the tested data, as well as the ability to fine-tune the material models while scrutinizing the trends shown in the underlying raw data. Advanced modeling features include the ability to tune the rate dependency as well as the initial response. Additional material models that are quite complex and difficult to calibrate are supported, including those for hyperelastic and viscoelastic behavior. As before, the written material cards are directly readable into the LS-DYNA software, but now they can also be stored and catalogued in a material card library for later reuse.

The use of CAE in design decision-making has created a need for proven simulation accuracy. The two areas where simulation touches the ground are with material data and experimental verification and validation (V&V). Precise, well designed and quantitative experiments are key to ensure that the simulation initiates with correct material behavior. Similar validation experiments are needed to verify simulation and manage the risk associated with this predictive technology.

As part of Cornell University's mechanical engineering curriculum and study of classical beam theory, an aluminium beam is deformed to a specific load. Theoretical strains are calculated at certain points along the beam using beam theory, and then verified by using strain gauges placed at these points on the beam. This experiment is then extended to simulation of the same test setup in simulation software, where strains are analyzed at the same points. Discrepancies between the simulation, theory, and strain gauge results have often plagued the test, especially when incorporating more complex beam design. Through use of digital image correlation (DIC) it is possible to pinpoint some of the problem areas in the beam analysis and provide a better understanding of the localized strains that occur at any point in the deformed beam. The use of DIC provides a full field validation of simulation data, rather than a single spot check that strain gauges can provide. This validation technique helps to eliminate error that is associated with strain gauge placement and the possibility of missing strain hot spots that can arise when analyzing complex deformations or geometries.

DatapointLabs' TestPaks (material testing + model calibration + Abaqus input decks) for rate-dependent, hyperelastic, viscoelastic, NVH, and the use of Abaqus CAE Modeler to transform raw data into material cards will be presented. A representative from Idiada will present a case study explaining the use of DatapointLabs’ material data and TestPaks for simulation.

We present a perspective on material modeling as applied to mold analysis requirements. Melt-solid transitions and the case for a unified material model are discussed, along with prediction of post-filling material behavior and shrinkage, and the impact of viscous heating on flow behavior and material degradation.

Many LS-DYNA models are used for plastics crash simulation. However, common models are not designed for plastics. We present best practices developed for adapting common models to plastics, as well as best testing protocols to generate clean, accurate rate-dependent data.

With the recent changes in the crashworthiness requirements for US automobiles for improved safety, design engineers are being challenged to design interior trim systems comprised of polymeric materials to meet these new impact requirements. Impact analysis programs are being used increasingly by designers to gain an insight into the final part performance during the design stage. Material models play a crucial role in these design simulations by representing the response of the material to an applied stimulus. In this work, we seek to develop novel test methods to generate high speed stress-strain properties of plastics, which can be used as input to structural analysis programs...